This invention relates generally to electronic weighing scales, and more specifically relates to an electronic counting scale adapted to make an accurate determination of the number of individual units present in a sample provided to the said scale, which sample contains a group of such individual units.
In numerous industrial and commercial applications, a requirement exists for effecting a rapid and accurate determination of the number of unit pieces or articles present in a relatively large group of such individual units. Thus for example, a manufacturer or shipper of small electronic components, or of relatively small hardware pieces such as washers or the like, may in the course of operations, require an accurate count of the number of individual units present in a large group of such like pieces.
In the past, various mechanically-actuated counting balances have been known for application to the aforementioned purposes. Mechanical devices of this type commonly, for example, utilize a pair of weighing platforms or cradles. A single article may be emplaced on one of the said platforms, with the plurality of the identical articles being positioned on the alternate platform. By such an arrangement, it is possible (after calibration) to determine the number of articles on the alternate of the mentioned platforms--i.e. in that the balance point is a function of the number of grouped units.
In general, such mechanically-actuated devices as above described, have proved to be relatively undesirable in continuous operation. They are, among other things, complex in structure, tend to require a high degree of attention and maintenance; and are furthermore, difficult and relatively time-consuming to operate.
More recently, counting scales have been disclosed based upon modern electronic technology, with a load cell providing the desired inputs to the electronic circuitry. Thus, for example, in U.S. Pat. No. 4,043,412, a counting scale is disclosed which utilizes a single such load cell--which determines the weights of both a standardization sample and of the unknown quantity of articles in a group which is thereafter presented to the device.
While electronic counting scales, including devices such as disclosed in the aforementioned U.S. Pat. No. 4,043,412, have indeed been found effective in achieving their objectives, the versatility and dependability of such apparatus have been less than desired in a number of respects. In many such prior art devices for example, relatively conventional load cell structures are utilized, commonly based upon parallelogram flexure structures. Most of these prior art flexure structures include strain gauges at all flexing corners, thereby rendering it extremely difficult to compensate for gauge positioning errors; the said prior art structures are, further, subject to generation of second-order errors upon offset loading of the weight-receiving platform.
Further, the prior art electronic counting scales such as have been previously discussed, have been poorly adapted to use with a wide range of weight loads, i.e. generally, a given such device is adapted for use in counting groups of articles within a fairly narrowly-prescribed total weight range.
Furthermore, from a purely electronic viewpoint, numerous of these prior art electronic counting scales have been relatively lacking in long-term stability, and in features assuring accuracy and stability in count--as the number of objects successively added to the scale for counting is accumulated.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide an electronic counting scale possessing simplicity and dependability of operation, and including features enabling highly stable operation over an extended period, and dependable, accurate counts--even as the number of objects accumulated on the weight platform continues to increase.
It is a further object of the present invention, to provide an electronic counting scale of the aforementioned character, which can be based upon an electronic unit including substantially all of the electronic circuitry, displays, and actuating switches and the like, which unit is combined with a separable module including the load cell and associated sample-receiving platform and the like, whereby a plurality of differing capacity base modules may be utilized interchangeably with the said electronic unit--thereby increasing the versatility and utility of the said scale apparatus.
It is a further object of the present invention, to provide an electronic counting scale of the aforementioned character, which incorporates a load cell based upon a parallelogram flexure--which load cell design, however, is uniquely free of second-order errors generated from offset loading of the force-receiving platform; which load cell structure is further, adapted for trimming to compensate for small symmetry errors present in the load cell as originally fabricated and assembled.
It is a still further object of the present invention, to provide an electronic counting scale as above discussed, which includes highly effective auto-zero tracking means in the electronic circuitry--to thereby provide a valid zero for extended periods, independent of drift of the electronic components.
It is a yet further object of the invention, to provide an electronic counting scale as aforesaid, which includes operator-actuatable means for periodically updating the unit weight being maintained in memory as the standard for comparison with the unknown group, to reflect the larger standardization groups which become available during measuring runs, thereby enabling increased accuracy in count for unknown groups being measured by the scale.